Blue-green algae are actually types of bacteria known as Cyanobacteria. In external appearance and requirements for light, nutrients and carbon dioxide, they are similar to algae. They normally look green and sometimes may turn bluish when scums are dying.
Blue-green algae are very small organisms and can be seen with the aid of a microscope as single cells, accumulations of cells (colonies) or filaments of cells (trichomes). Certain types of blue-green algae have tiny gas vesicles in their cells, allowing them to float to the surface or sink to the bottom in response to changing light and nutrient availability. This buoyancy-regulating mechanism gives the blue-green algae a competitive advantage in obtaining light and nutrients.
Blue-green algae thrive on warm weather and nutrient levels arising from the use of artificial fertilisers containing phosphorus and/or nitrogen. These fertilisers are used on catchment farming and end up leaching into river systems that discharge into the lakes. For these reasons algal blooms are becoming a regular annual event within the Gippsland Lakes. Blooms often persist for several weeks, sometimes months, depending mainly on the weather or flow conditions. Cooler, windy weather or increased flow may reduce or prevent blooms from occurring.
As the bloom dies, the cells tend to leak toxins into the surrounding water. Once released, some toxins may persist for more than three months before sunlight and the natural population of bacteria in the water degrade them. Toxins can build up in fish and shellfish and are dangerous to the health of other animals and to humans if consumed.
The 2011/2012 summer bloom saw the banning of fish consumption from the Gippsland Lakes which impacted on the regions tourism, recreational and commercial fishing industry.